It is estimated that the energy costs to heat the nation's 5.7 million pools and spas run in the billions of dollars annually. Outdoor pools use high amounts of energy to heat water, which loses heat during the evening and through evaporation. Indoor pools use a lot of energy for systems that remove evaporation-caused humidity.

A pool cover can dramatically reduce energy use by a swimming pool. A pool covered just half the time can save up to 50 percent in annual energy costs.

A basic pool cover with enough material for a 30-foot by 15-foot pool will cost around $80. A storage reel for the cover costs about $160. A high quality insulating pool blanket can cost up to $700 for a 30-foot by 15-foot pool.

Reducing the water temperate just four degrees, from 82 to 78 degrees, can cut your pool's natural gas costs by as much as 40 percent. If you live in a sunny region you might consider installing a solar heating system for your pool.

Table 1 shows some savings estimates for pool covers. To use this table to estimate costs for you pool, divide your pool's surface area (sq. ft.) by 1,000 then multiply this number by the heating costs and savings figures for your pool type in the location that most similarly matches your local climate.

For example let’s say you live in Chicago and have an outdoor pool that is 30 x 15 feet. Your pool’s surface area is 450 square feet. Divide 450 by 1000 to get a value of 0.45. From the table you find the annual heating costs for an outdoor pool in Chicago is $1,024. Multiply this by 0.45 to get an estimated annual heating cost of $461.